Piezoelectric transducer for an energy-harvesting system

ABSTRACT

A piezoelectric transducer for energy-harvesting systems includes a substrate, a piezoelectric cantilever element, a first magnetic element, and a second magnetic element, mobile with respect to the first magnetic element. The first magnetic element is coupled to the piezoelectric cantilever element. The first magnetic element and the second magnetic element are set in such a way that, in response to relative movements between the first magnetic element and the second magnetic element through an interval of relative positions, the first magnetic element and the second magnetic element approach one another without coming into direct contact, and the interaction between the first magnetic element and the second magnetic element determines application of a force pulse on the piezoelectric cantilever element.

BACKGROUND Technical Field

The present disclosure relates to a piezoelectric transducer for anenergy-harvesting system and to a method for harvesting energy through apiezoelectric transducer.

Description of the Related Art

The disclosure is particularly suited to the production of piezoelectricmicrotransducers that may be used in miniaturized energy-harvestingsystems capable of supplying, among others, electronic components and/ordevices, such as low-consumption sensors and actuators, frequently usedin portable electronic devices, such as cellphones, tablet computers,portable computers (laptops), video cameras, photographic cameras,consoles for videogames, and so forth.

As is known, systems for collecting energy from environmental-energysources (also referred to as energy harvesting or energy scavengingsystems) have aroused and continue to arouse considerable interest in awide range of fields of technology. Typically, energy-harvesting systemsare designed to harvest (or scavenge), store, and transfer energygenerated by mechanical sources to a generic load of an electrical type.In this way, the electrical load does not use batteries or other supplysystems that are frequently cumbersome, have low resistance tomechanical stresses and entail maintenance costs for replacementoperations. Furthermore, systems for harvesting environmental energy areof considerable interest for devices that are in any case provided withbattery supply systems, which, however, have a rather limited autonomy.This is the case, for example, of many portable electronic devices thatare increasingly becoming widely used, such as cellphones, tablets,portable computers (laptops), video cameras, photographic cameras,consoles for videogames, etc. Systems for harvesting environmentalenergy may be used for supplying components or devices in order toreduce the energy absorbed from the battery and, in practice, increasethe autonomy.

Environmental energy may be harvested from several available sources andconverted into electrical energy by appropriate transducers. Forinstance, available energy sources may be mechanical or acousticvibrations or, more in general, forces or pressures, chemical-energysources, electromagnetic fields, environmental light, thermal-energysources.

For harvesting and conversion piezoelectric transducers may, amongothers, be used.

Piezoelectric transducers are in general based upon a microstructurecomprising a supporting body, connected to which are piezoelectriccantilever elements, having at least one portion made of piezoelectricmaterial. The free ends of the piezoelectric cantilever elements, towhich additional masses can be connected, oscillate elastically inresponse to movements of the supporting body or to vibrationstransmitted thereto. As a result of the movements of bending andextension during the oscillations, the piezoelectric material produces acharge that can be harvested and stored in a storage element.

In miniaturized transducers, however, the use of just the piezoelectriccantilever elements and the additional masses does not enable adequatelevels of efficiency to be achieved. In practice, the conversion ofkinetic energy is not satisfactory because the natural frequency of thesystem formed by the piezoelectric cantilever element and by theadditional mass is too different from the typical environmentalfrequencies that can be transduced.

To improve the efficiency of piezoelectric transducers, it has beenproposed to use a movable mass separate from the piezoelectriccantilever elements and magnets that enable temporary coupling of themovable mass and piezoelectric cantilever elements. The magnets arearranged in part on the movable mass and in part on the piezoelectriccantilever elements and are oriented so as to exert attractive forces.The movable mass is constrained to the supporting body so as to be ableto come into contact with the piezoelectric cantilever elements andenable coupling of the magnets. The piezoelectric cantilever elementsare drawn along in motion by the movable mass and undergo deformationuntil the elastic return force exceeds the magnetic force. At thispoint, the magnets separate, and the action of the magnetic force on thepiezoelectric cantilever elements ceases almost instantaneously as themovable mass moves away, allowing the elastic force alone to act. Inpractice, this is equivalent to applying a force pulse on thepiezoelectric cantilever elements, which are hence stimulated over awide frequency band, which also includes the resonance frequency.

Albeit far better from the efficiency standpoint, the devices describedpresent, however, some limits in terms of reliability. In fact, eachoscillation of the movable mass causes impact between the magnets of themovable mass itself and the magnets of the piezoelectric cantileverelements. Even though the frequency of oscillation of the movable massis low (generally less than about 10 Hz), in the long run repetition ofthe impact may cause damage to the microstructure. In particular,microcracks may be formed, which rapidly propagate until they render thetransducer unserviceable.

BRIEF SUMMARY

The present disclosure is directed to a piezoelectric transducer for anenergy-harvesting system and a method for harvesting energy through apiezoelectric transducer that enables the limitations described to beovercome or at least attenuated.

One embodiment of the present disclosure is a transducer that includes asubstrate, a moveable mass elastically coupled to the substrate, aplurality of cantilever piezoelectric elements extending from thesubstrate towards the moveable mass, a plurality of first magneticelements at free ends of respective cantilever piezoelectric elements,and a plurality of second magnetic elements on the moveable mass, eachsecond magnetic element being aligned with cantilever piezoelectricelements in a rest condition.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the disclosure, some embodiments thereofwill now be described, purely by way of non-limiting example and withreference to the attached drawings, wherein:

FIG. 1 is a simplified block diagram of an energy-harvesting system;

FIG. 2 is a simplified top plan view of a piezoelectric transduceraccording to one embodiment of the present disclosure and incorporatedin the energy-harvesting system of FIG. 1, the piezoelectric transducerbeing represented in a first operating configuration;

FIG. 3 shows the piezoelectric transducer of FIG. 2 in a secondoperating configuration;

FIG. 4 shows the piezoelectric transducer of FIG. 2 in a third operatingconfiguration;

FIG. 5 shows the piezoelectric transducer of FIG. 2 in a fourthoperating configuration;

FIG. 6 is a graph that shows quantities regarding the piezoelectrictransducer of FIG. 2;

FIG. 7 is a simplified top plan view of a piezoelectric transduceraccording to a different embodiment of the present disclosure, in afirst operating configuration;

FIG. 8 shows the piezoelectric transducer of FIG. 7 in a secondoperating configuration;

FIG. 9 is a top plan view, with parts removed for clarity, of apiezoelectric transducer according to a different embodiment of thepresent disclosure;

FIG. 10 is an enlarged cross-sectional view through the piezoelectrictransducer of FIG. 9, taken along the line X-X of FIG. 9;

FIG. 11 is a top plan view, with parts removed for clarity, of apiezoelectric transducer according to a further embodiment of thepresent disclosure;

FIG. 12 is an enlarged cross-sectional view through the piezoelectrictransducer of FIG. 11, taken along the line XII-XII of FIG. 12;

FIG. 13 is a top plan view, with parts removed for clarity, of apiezoelectric transducer according to a further embodiment of thepresent disclosure; and

FIG. 14 is an enlarged cross-sectional view through the piezoelectrictransducer of FIG. 13, taken along the line XIV-XIV of FIG. 13.

DETAILED DESCRIPTION

With reference to FIG. 1, an energy-harvesting system is designated as awhole by the reference number 1. The energy-harvesting system 1 isparticularly, but not exclusively, suited to being used for supplyingelectronic components and/or devices, such as low-consumption sensorsand actuators, which ever more frequently used in portable electronicdevices, such as cellphones, tablets, portable computers (laptops),video cameras, photographic cameras, consoles for videogames, etc.

Electronic components and devices supplied through the energy-harvestingsystem 1 are rendered self-sufficient and do not absorb energy from themain supply system (normally a battery), which hence has greaterautonomy, to the advantage of users.

Furthermore, in some applications the energy-harvesting system 1 may beused both as main supply source, and as auxiliary supply source for theelectronic components and/or devices referred to above. In this case,the energy-harvesting system 1 may be set alongside a conventionalsupply system, for example a battery supply, and go into operation whenthe main supply system runs down or presents malfunctioning.

The energy-harvesting system 1 comprises a transducer 2, a harvestinginterface 3, a storage element 5, a selective-connection device 6, and avoltage regulator 7. Furthermore, an output of the voltage regulator 7supplies an electrical load 8.

The transducer 2 supplies a harvesting voltage V_(H) in response toenergy provided by an environmental-energy source 4 external to theharvesting system 1. The transducer 2 is a piezoelectric transducer thatsupplies a harvesting voltage V_(H) in response to mechanical vibrationstransmitted from the outside environment and will be described ingreater detail hereinafter.

The harvesting interface 3, when supplied by the storage element 5,receives the harvesting voltage V_(H) from the transducer 2 and suppliesa charge current I_(CH) to the storage element 5. The energy stored inthe storage element 5 increases as a result of the charge current I_(CH)and produces a storage voltage V_(ST).

The selective-connection device 6 selectively connects and disconnects asupply input 3 a of the harvesting interface 3 and the storage element 5on the basis of the response of the transducer 2. More precisely, whenthe harvesting voltage V_(H) exceeds an activation threshold V_(A), thatrepresents a state in which the transducer 2 is active and receivesenvironmental energy from outside, the selective-connection device 6connects the harvesting interface 3 to the storage element 5, so thatthe harvesting interface 3 receives the storage voltage V_(ST) presenton the storage element 5.

The harvesting interface may thus use the harvesting voltage V_(H) forcharging the storage element 5.

Instead, when the transducer 2 does not receive environmental energy andthe harvesting voltage V_(H) is below the activation threshold V_(A),the selective-connection device 6 disconnects the harvesting interface 3from the storage element 5, so that the consumption of energy of theharvesting interface 3 ceases.

In one embodiment, in particular, the selective-connection devicecomprises a switch 10 and a driving stage 11, configured to drive theswitch 10 on the basis of the comparison between the harvesting voltageV_(H) and the activation threshold V_(A).

The voltage regulator 7 receives the storage voltage V_(ST) and suppliesa regulated supply voltage V_(DD) to the electrical load 8.

The selective-supply device 6 substantially makes it possible to reduceto zero the consumption of the harvesting interface 3 in the absence ofactivity of the transducer 2 and hence prevents dissipation of energyaccumulated on the storage element 5, when the harvesting system 1 isnot in a condition to receive energy from the environment.

According to one embodiment of the disclosure, illustrated in FIGS. 2-5,the transducer 2 comprises a microstructure including a supporting body15, a movable mass 16, and an oscillating piezoelectric cantileverelement 17. The supporting body 15, the movable mass 16, and part of thepiezoelectric cantilever element 17 are made of semiconductor material,for example monocrystalline silicon.

The supporting body 15 may be a monolithic semiconductor body, or elsemay be obtained from the union of two or more semiconductor dice,possibly with the interposition of bonding layers and/or dielectriclayers.

The movable mass 16 is elastically coupled to the supporting body 15 bya system of suspensions 18, here schematically represented by a springand a damper. The suspensions 18 are configured to enable oscillationsof the movable mass 16 along one or more axes of transduction at a firstresonance frequency (main resonance frequency of the movable mass 16constrained by the suspensions 18), for example less than 10 Hz. In theexample described, in particular, the movable mass 16 (the position ofwhich during an oscillation is indicated by a dashed line in the graphprovided by way of example in FIG. 6) can translate along a transductionaxis X parallel to a face 15 a of the supporting body 15 between a firstend-of-travel position X₁ and a second end-of-travel position X₂, wherethere are set stop elements (not shown) in order to prevent undesirableand potentially harmful over-shooting. The movable mass 16 may comprise,in addition to semiconductor structures, also layers or portions made ofheavy metals, such as lead or tungsten, in order to improve theenergy-harvesting efficiency.

In one embodiment, the piezoelectric cantilever element 17 is defined bya piezoelectric layer 20 formed on a face of a supporting plate 21 madeof semiconductor material, integral with the supporting body 15. Thepiezoelectric layer 20 and the supporting plate 21 are coupled in such away that any bending of the supporting plate 21 causes correspondingdeformations of the piezoelectric layer 20. Furthermore, thepiezoelectric layer 20 is connected to a contact pad 22 on thesupporting body 15.

The piezoelectric cantilever element 17 is anchored to the supportingbody 15 and projects from the supporting body 15 in the direction of themovable mass 16, as illustrated in FIGS. 2-4.

Furthermore, the piezoelectric cantilever element 17 extends in adirection transverse, for example substantially perpendicular, to thetransduction axis X, which coincides with the direction of motion of themovable mass 16. The length of the piezoelectric cantilever element 17is such that a free end thereof occupies a position in the proximity ofthe movable mass 16 at least in an interval of positions of the movablemass 16 along the transduction axis X, without, however, any contactbetween the movable mass 16 and the piezoelectric cantilever element 17.Preferably, between the movable mass 16 and the piezoelectric cantileverelement 17 there is always present at least a minimum distance L_(G)(FIG. 2).

The ensemble constituted by the piezoelectric cantilever element 17 andthe piezoelectric layer 20 is elastically deformable and can oscillatewith respect to a rest position with a second resonance frequency (mainresonance frequency of the piezoelectric cantilever element 17), higherthan the first resonance frequency by at least one order of magnitudeand preferably comprised between 1 kHz and 10 kHz. In one embodiment,the second resonance frequency is approximately 1 kHz.

A first magnetic element 25 and a second magnetic element 26 are set,respectively, at the free ends of the piezoelectric cantilever element17 and on the movable mass 16, on an edge adjacent to the piezoelectriccantilever element 17. The magnetic characteristics of the firstmagnetic element 25 and of the second magnetic element 26 are selectedin such a way that a magnetic force deriving from the interaction of thefirst magnetic element 25 and of the second magnetic element 26 issufficient to deform the piezoelectric cantilever element 17 uponpassage of the movable mass 16 through an interval of interactionpositions ΔX around a rest position X₀ of the piezoelectric cantileverelement 17. Furthermore, the magnetic characteristics of the firstmagnetic element 25 and of the second magnetic element 26 are selectedso that, outside the interval of interaction positions ΔX, the elasticreturn force due to deformation of the piezoelectric cantilever element17 prevails over the magnetic force between the first magnetic element25 and the second magnetic element 26. Furthermore, outside the intervalof interaction positions ΔX the magnetic force rapidly decays as aresult of the increasing distance.

When the supporting body 15 varies its condition of motion or issubjected to impact or vibrations, the movable mass 16 oscillates alongthe transduction axis X. Upon passage through the interval ofinteraction positions ΔX, albeit in the absence of direct contact, themagnetic interaction between the first magnetic element 25 and thesecond magnetic element 26 causes deformation of the piezoelectriccantilever element 17. When the movable mass 16 passes beyond theinterval of interaction positions ΔX, the elastic return force prevails,and the magnetic force decays until it soon becomes negligible. Thepiezoelectric cantilever element 17 thus receives a force substantiallyof an impulsive type, which produces stimuli over a wide frequency band,including the second resonance frequency. The piezoelectric cantileverelement 17 starts to oscillate as a result of the pulse received, asindicated with a solid line in FIG. 6, and the corresponding deformationof the piezoelectric layer 20 produces a voltage that can be picked upat the pad 22 and used for charging the storage element 5.

It is to be noted that the magnetic forces between the first magneticelement 25 and the second magnetic element 26 may be indifferently of anattractive or repulsive type, provided that the interaction determines aforce pulse on the piezoelectric cantilever element 17 during traversalof the interval of interaction positions ΔX. In one embodiment, themagnetic forces may be attractive when the second magnetic element 26 islocated on one side of the first magnetic element 25 and repulsive whenthe second magnetic element 26 is located on the opposite side.

Energy harvesting is efficient because the oscillations of the movablemass 16 and the piezoelectric cantilever element 17 are decoupled, andhence the piezoelectric cantilever element 17 may vibrate at its naturalresonance frequency. Furthermore, the force pulses are transmitted tothe piezoelectric cantilever element 17 without direct contact with themovable mass 16 or with the first magnetic element 25 placed thereon.The parts of the microstructure are hence not subjected to impact duringoperation, to the advantage of reliability.

According to one embodiment, illustrated in FIGS. 7 and 8, apiezoelectric transducer 100, which may be used in the energy-harvestingsystem 1 instead of the piezoelectric transducer 2, comprises asupporting body 115, a movable mass 116, and an oscillatingpiezoelectric cantilever element 117. The supporting body 115, themovable mass 116, and part of the piezoelectric cantilever element 117are made of semiconductor material, for example monocrystalline silicon.

The movable mass 116 is elastically connected to the supporting body 115by a system of suspensions 118, fixed to an anchorage 119 and configuredto enable oscillations of the movable mass 116 along a transduction axisX′ parallel to a face 115 a of the supporting body 115 with a firstresonance frequency, for example less than 10 Hz.

The piezoelectric cantilever element 117 is defined by a piezoelectriclayer 120 formed on a face of a supporting plate 121 of semiconductormaterial, integral with the movable mass 116. The piezoelectric layer120 and the supporting plate 121 are shaped so that any bending of thesupporting plate 121 causes corresponding deformations of thepiezoelectric layer 120. Furthermore, the piezoelectric layer 120 isconnected to a contact pad 122 on the supporting body 115 through thesuspensions 118 and the anchorage 119, which may themselves be madeconductive by appropriate doping or else may be coated with a metallayer.

The piezoelectric cantilever element 117 projects from the movable mass116 in a direction parallel to a face 115 a of the supporting body 115and substantially perpendicular to the transduction axis X.

The ensemble of the piezoelectric cantilever element 117 and thepiezoelectric layer 120 is elastically deformable and can oscillate withrespect to a rest position at a second resonance frequency, higher thanthe first resonance frequency.

A first magnetic element 125 is set at the free end of the piezoelectriccantilever element 117.

A second magnetic element 126 is set on the supporting body 115, alongthe path of a free end of the piezoelectric cantilever element 117, sothat the free end of the piezoelectric cantilever element 117 passesover the first magnetic element 125 or in its immediate vicinity,without in any case direct contact, however.

The magnetic characteristics of the first magnetic element 125 andsecond magnetic element 126 are selected so that a magnetic forcederiving from the interaction of the first magnetic element 125 and ofthe second magnetic element 126 is sufficient to deform thepiezoelectric cantilever element 117 upon passage of the piezoelectriccantilever element 117 in the proximity of the second magnetic element126. Furthermore, the magnetic characteristics of the first magneticelement 125 and of the second magnetic element 126 are selected so that,outside of an interval of interaction positions ΔX′, the elastic returnforce due to deformation of the piezoelectric cantilever element 117prevails over the magnetic force between the first magnetic element 125and the second magnetic element 126. Furthermore, outside of theinterval of interaction positions ΔX′ the magnetic force decays rapidlyas a result of the increasing distance.

FIGS. 9 and 10 illustrate a piezoelectric transducer 200 according to adifferent embodiment of the present disclosure. The transducer 200comprises a supporting body 215, a movable mass 216, and a plurality ofoscillating piezoelectric cantilever elements 217. The supporting body215, the movable mass 216, and parts of the piezoelectric cantileverelements 217 are made of semiconductor material, for examplemonocrystalline silicon. Also illustrated in FIG. 10 is a protective cap250 arranged so as to cover the movable mass 216.

The supporting body 215 has a recess 215 b accessible through a face 215a. The recess 215 b houses the movable mass 216, which, in a restconfiguration, is flush with the face 215 a.

The movable mass 216, which has a substantially rectangular or squareshape, is elastically connected to the supporting body 215 by a systemof suspensions 218, configured so as to enable oscillations of themovable mass 216 along a transduction axis Z at a first resonancefrequency. In the example described, in particular, the transductionaxis Z is perpendicular to a face 215 a of the supporting body 215. Thetransducer 200 is consequently of the so-called “out of plane” type. Byway of non-limiting example, the movable mass 216 may have a length andwidth of between 400 and 800 μm, while the thickness may reach 400 μm.

The piezoelectric cantilever elements 217 are defined by piezoelectriclayers 220 formed on faces of respective supporting plates 221 ofsemiconductor material, integral with the supporting body 215 and havingfaces parallel to the face 215 a of the supporting body 215 itself. Thepiezoelectric layers 220 and the supporting plates 221 are shaped sothat any bending of the supporting plates 221 causes correspondingdeformations of the respective piezoelectric layers 320. Furthermore,the piezoelectric layers 220 are connected to respective contact pads222 set on the supporting body 215.

The piezoelectric cantilever elements 217 project from the supportingbody 215, in particular from the perimeter of the recess 215b, towardsthe movable mass 216, in a direction substantially perpendicular to thetransduction axis Z and parallel to the face 215 a of the supportingbody 215. In greater detail, the piezoelectric cantilever elements 217are comb-fingered in groups, each of which faces a respective side ofthe movable mass 216. The length of the piezoelectric cantileverelements 217 is such that the respective free ends are in the proximityof the movable mass 216 at least in an interval of positions of themovable mass 216 along the transduction axis Z, without, however, anycontact between the movable mass 216 and the piezoelectric cantileverelements 217.

The ensemble of each piezoelectric cantilever element 217 and of therespective piezoelectric layer 220 is elastically deformable and canoscillate with respect to a rest position at a second resonancefrequency, higher than the first resonance frequency. The oscillationsare substantially in planes perpendicular to the face 215 a of thesupporting body 215.

First magnetic elements 225 and second magnetic elements 226 are set,respectively, at the free ends of the piezoelectric cantilever elements217 and on the movable mass 216.

The second magnetic elements 226, in particular, are arranged along theperimeter of the movable mass 216 and are each aligned to a respectivepiezoelectric cantilever element 217. In one embodiment (notillustrated) a single second magnetic element is present and runs alongthe entire perimeter of the movable mass 216.

The first magnetic elements 226 are set at the free ends of respectivepiezoelectric cantilever elements 217 and are hence in the proximity ofcorresponding second magnetic elements 226 at least when the movablemass 216 is in an interval of interaction positions ΔZ around a restposition Z₀ of the piezoelectric cantilever elements 217.

The magnetic characteristics of the first magnetic elements 225 and thesecond magnetic elements 226 are selected in such a way that a magneticforce deriving from the interaction of the first magnetic elements 225and of the second magnetic elements 226 is sufficient to deform thepiezoelectric cantilever elements 217 upon passage of the movable mass216 through the interval of interaction positions ΔZ. Furthermore, themagnetic characteristics of the first magnetic elements 225 and of thesecond magnetic elements 226 are selected so that, outside the intervalof interaction positions ΔZ, the elastic return force due to deformationof the piezoelectric cantilever element 217 prevails over the magneticforce between the first magnetic elements 225 and the second magneticelements 226. Outside the interval of interaction positions ΔZ, themagnetic force decays rapidly as a result of the increasing distance. Inthis way, passage of the movable mass 216 through the interval ofinteraction positions ΔZ, transmits, through contactless interactionsbetween the first magnetic elements 225 and the second magnetic elements226, a force pulse that sets the piezoelectric cantilever elements 217in vibration.

The embodiment described enables efficient exploitation of the kineticenergy associated to the movable mass 216 for conversion into electricalenergy, in particular thanks to the high density of piezoelectriccantilever elements 217 that it is possible to obtain thanks to moderntechniques of machining of semiconductors.

FIGS. 11 and 12 illustrate a piezoelectric transducer 300 according to adifferent embodiment of the present disclosure. The transducer 300comprises a supporting body 315, a movable mass 316, and a plurality ofoscillating piezoelectric cantilever elements 317. The supporting body315, the movable mass 316, and parts of the piezoelectric cantileverelements 317 are made of semiconductor material, for examplemonocrystalline silicon. Also illustrated in FIG. 12 is a protective cap350 arranged to cover the movable mass 316.

The supporting body 315 has a recess 315 b accessible through a face 315a. The recess 315 b houses the movable mass 316, which, in a restconfiguration, is flush with the face 315 a.

The movable mass 316 has a substantially rectangular or square shape andis elastically connected to the supporting body 315 by a system ofsuspensions 318, configured to enable oscillations of the movable mass316 along a transduction axis Z′ at a first resonance frequency. In theexample described, in particular, the transduction axis Z′ isperpendicular to a face 315 a of the supporting body 315. The transducer300 is consequently of the so-called “out of plane” type.

Present for each side of the movable mass 316 is a respectivepiezoelectric cantilever element 317, which extends, in one direction,from the supporting body 315 as far as into the proximity of the movablemass 316 and, in the perpendicular direction, substantially along theentire respective side of the movable mass 316. The piezoelectriccantilever elements 317 are defined by piezoelectric layers 320 formedon faces of respective flexible supporting plates 321 made ofsemiconductor material, integral with the supporting body 315 and havingfaces parallel to the face 315 a of the supporting body 315 itself.

The piezoelectric layers 320 and the supporting plates 321 are shaped sothat any bending of the supporting plates 321 causes correspondingdeformations of the respective piezoelectric layers 320. Furthermore,the piezoelectric layers 320 are connected to respective contact pads322 on the supporting body 315.

The ensemble of each piezoelectric cantilever element 317 and of therespective piezoelectric layer 320 is elastically deformable and canoscillate with respect to a rest position at a second resonancefrequency, higher than the first resonance frequency. The oscillationsare substantially in planes perpendicular to the face 315 a of thesupporting body 315.

First magnetic elements 325 and second magnetic elements 326 are set,respectively, at the free ends of the piezoelectric cantilever elements317 and on the movable mass 316. In one embodiment, the first magneticelements 325 and second magnetic elements 326 are continuous strips. Thefirst magnetic elements 325 extend along the entire edge of therespective piezoelectric cantilever elements 317. The second magneticelements 326 have a length substantially equal to the length of therespective coupled first magnetic elements 325.

The first magnetic elements 326 are set at the free ends of respectivepiezoelectric cantilever elements 317 and hence are in the proximity ofcorresponding second magnetic elements 326 at least when the movablemass 316 is within an interval of interaction positions ΔZ around a restposition Z₀ of the piezoelectric cantilever elements 317.

The magnetic characteristics of the first magnetic elements 325 and ofthe second magnetic elements 326 are selected so that a magnetic forcederiving from the interaction of the first magnetic elements 325 and ofthe second magnetic elements 326 is sufficient to deform thepiezoelectric cantilever elements 317 upon passage of the movable mass316 through the interval of interaction positions ΔZ. Outside theinterval of interaction positions ΔZ, instead, the elastic return forcedue to the deformation of the piezoelectric cantilever element 317prevails over the magnetic force between the first magnetic elements 325and the second magnetic elements 326.

Consequently, passage of the movable mass 316 through the interval ofinteraction positions ΔZ, transmits, through contactless interactionsbetween the first magnetic elements 325 and the second magnetic elements326, a force pulse that sets the piezoelectric cantilever elements 317in vibration.

The embodiment described enables limitation of the number of connectionsfor harvesting of the mechanical energy and its conversion intoelectrical energy. Furthermore, the area of piezoelectric materialavailable is further increased, given the same efficiency, andmanufacture is simplified.

Illustrated in FIGS. 13 and 14 is a piezoelectric transducer 400according to a further embodiment of the present disclosure.

The piezoelectric transducer 400 comprises a supporting body 415, amovable mass 416, and a plurality of oscillating piezoelectriccantilever elements 417. The supporting body 415, the movable mass 416,and part of the piezoelectric cantilever elements 417 are made ofsemiconductor material, for example monocrystalline silicon. Alsoillustrated in FIG. 14 is a protective cap 450 arranged to cover themovable mass 416.

The supporting body 415 has a face 415 a in which a circular recess 415b is provided. The recess 415 b houses the movable mass 416, flush withthe face 415 a.

Also the movable mass 416 has a circular shape and is connected to thesupporting body by a system of suspensions 418 connected to a centralanchorage 419. The suspensions 418 are configured so as to enable themovable mass 416 to perform oscillating rotational movements, at a firstresonance frequency, about a transduction axis Z″ perpendicular to themovable mass 416 itself (in practice, perpendicular to the face 415 a ofthe supporting body 415).

The piezoelectric cantilever elements 417 are defined by piezoelectriclayers 420 formed on faces of respective supporting plates 421 made ofsemiconductor material, integral with the supporting body 415 and havingfaces perpendicular to the face 415 a of the supporting body 415 itself.The piezoelectric layers 420 and the supporting plates 421 are shaped sothat any bending of the supporting plates 421 causes correspondingdeformations of the respective piezoelectric layers 420. Furthermore,the piezoelectric layers 420 are connected to respective contact pads422 set on the supporting body 415.

The piezoelectric cantilever elements 417 project from the perimeter ofthe recess 415 b in a radial direction inwards and extend as far as intothe proximity of the movable mass 416, from which they are separated byradial gaps 401. The piezoelectric cantilever elements 417 are hence notin direct contact with the movable mass 416, either in a rest conditionor in normal conditions of motion of the movable mass 416 itself

The ensemble of each piezoelectric cantilever element 417 and of therespective piezoelectric layer 420 is elastically deformable and canoscillate with respect to a rest position at a second resonancefrequency, higher than the first resonance frequency. The plane ofoscillation of the piezoelectric cantilever elements 417 issubstantially parallel to the face 415 a of the supporting body 415.

First magnetic elements 425 and second magnetic elements 426 are set,respectively, at the free ends of the piezoelectric cantilever elements417 and on the movable mass 416.

The second magnetic elements 426, in particular, are arranged along theperimeter of the movable mass 416 and are each aligned to a respectivepiezoelectric cantilever element 417, when the movable mass 416 is in arest angular position.

The first magnetic elements 425 are set at the free ends of respectivepiezoelectric cantilever elements 417 and hence are in the proximity ofcorresponding second magnetic elements 426 at least when the movablemass 416 is in an interval of interaction angular positions Δθ around arest position θ₀. In one embodiment, in the rest position θ₀ of themovable mass 416, the second magnets 426 are aligned to respectivepiezoelectric cantilever elements 417, which are in turn in restconditions. The direction of movement of the second magnetic elements426 is moreover perpendicular to the faces of the piezoelectriccantilever elements 417 (the path of the first magnetic elements 425 isin fact circular, whereas the piezoelectric cantilever elements 417extend in a radial direction).

The magnetic characteristics of the first magnetic elements 425 and ofthe second magnetic elements 426 are selected so that a magnetic forcederiving from the interaction of the first magnetic elements 425 and ofthe second magnetic elements 426 is sufficient to deform thepiezoelectric cantilever elements 417 during rotation of the movablemass 416 through the interval of interaction angular positions Δθ.Furthermore, the magnetic characteristics of the first magnetic elements425 and of the second magnetic elements 426 are selected so that,outside of the interval of interaction angular positions Δθ the elasticreturn force due to deformation of the piezoelectric cantilever element417 prevails over the magnetic force between the first magnetic elements425 and the second magnetic elements 426. Outside of the interval ofinteraction angular positions Δθ the magnetic force decays rapidly as aresult of the increasing distance. In this way, rotation of the movablemass 416 through the interval of interaction angular positions Δθtransmits, through contactless interactions between the first magneticelements 425 and the second magnetic elements 426, a force pulse thatsets the piezoelectric cantilever elements 417 in vibration.

Finally, it is evident that modifications and variations may be made tothe system and method described herein, without thereby departing fromthe scope of the present disclosure.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

1. A system, comprising: a piezoelectric transducer configured toharvest environmental energy and to convert harvested environmentalenergy into a harvesting electrical signal, the piezoelectric transducerincluding: a semiconductor substrate; a cantilever component having apiezoelectric element; a first magnetic element on the cantilevercomponent; and a second magnetic element configured to interact with thefirst magnetic element to move the cantilever component; a storageelement configured to store electrical energy from the piezoelectrictransducer; and a harvesting interface coupled to the piezoelectrictransducer and configured to provide a charge electrical signal to thestorage element as a function of the harvesting electrical signal. 2.The system of claim 1, further comprising: a movable mass elasticallycoupled to the substrate, the second magnetic element being on themovable mass and the cantilever component extending from a portion ofthe substrate.
 3. The system of claim 1, further comprising a drivingelement configured to receive the harvesting electrical signal and tocontrol a switch.
 4. The system of claim 3 wherein the driving elementis configured to selectively connect and disconnect the harvestinginterface to the storage element based on the piezoelectric transducer.5. The system of claim 4 wherein the driving element is configured toconnect the harvesting interface to the storage element when theharvesting electrical signal exceeds an activation threshold to chargethe storage element.
 6. A device, comprising: a substrate including arecess having a base and a sidewall, the base extending in a firstdirection, the sidewall extending in a second direction that istransverse to the first direction; a moveable mass coupled to the base,the movable mass configured move in the first direction; a plurality ofcantilever piezoelectric elements extending from the sidewall towardsthe moveable mass; a plurality of first magnetic elements on theplurality of cantilever piezoelectric elements, respectively; and aplurality of second magnetic elements on the moveable mass.
 7. Thedevice of claim 6 wherein the plurality second magnetic elements areconfigured to respectively interact with the plurality of first magneticelements, and respectively generate respective force pulses on theplurality of cantilever piezoelectric elements, respectively.
 8. Thedevice of claim 6 wherein the plurality of cantilever piezoelectricelements extend towards the movable mass without directly contacting themovable mass.
 9. The device of claim 6 wherein the movable mass has acircular shape, and the plurality of cantilever piezoelectric elementsextends in a radial direction.
 10. The device of claim 6 wherein themovable mass configured to rotate in the first direction.
 11. The deviceof claim 6, further comprising: an anchorage coupled to the base; and asuspension coupling the movable mass to the anchorage.
 12. The device ofclaim 6, further comprising: a cap on the substrate and overlying themoveable mass.
 13. A device, comprising: a substrate including asurface; a moveable mass coupled to the surface of the substrate, themoveable mass configured to move in a first direction; a cantileverpiezoelectric element coupled to the moveable mass, the cantileverpiezoelectric element extending in a second direction that is transverseto the first direction; and a first magnetic element on the cantileverpiezoelectric element; and a second magnetic element on the surface ofthe substrate, the first magnetic element being positioned on thecantilever piezoelectric element such that the first magnetic elementoverlies the second magnetic element when the moveable mass moves in thefirst direction.
 14. The device of claim 13, further comprising: ananchorage coupled to the surface of the substrate; and a suspensioncoupling the movable mass to the anchorage.
 15. The device of claim 14,further comprising: a contact pad on the surface of the substrate, thecontact pad being electrically coupled to the cantilever piezoelectricelement via the anchorage and the suspension.
 16. The device of claim 13wherein the cantilever piezoelectric element includes a supporting plateand a piezoelectric layer, and the piezoelectric layer is between thesupporting plate and the first magnetic element.
 17. The device of claim16 wherein the piezoelectric layer is spaced from the supporting plateby the first magnetic element in the first direction.